NEW YORK—Three European nations today joined California and a growing list of cities, regions and now countries to sign a first-of-its-kind agreement to limit global warming to less than 2 degrees Celsius.

Leaders from The Netherlands, Luxembourg and the United Kingdom endorsed the Under 2 MOU, as the agreement is known, at a ceremony Sunday at The Netherlands’ Permanent Mission to the United Nations. The three countries are among the first national endorsements of the Under 2 MOU, which added 14 new signatories at an event Thursday.

“The Dutch endorsement of the Under 2 MOU is an important step. Action by large states and provinces like California, Québec and Ontario is of vital importance to reduce CO2 emissions,” said Wilma Mansveld, The Netherlands Minister for the Environment. “The Under 2 MOU is exactly what it says: our best option to fight climate change and keep the temperature rise on earth below 2 degrees.”

To date, a total of 41 jurisdictions representing 19 countries and five continents have signed or endorsed the Under 2 MOU, collectively representing more than $12.3 trillion in GDP and 387 million people. If the signatories represented a single country, it would be the second largest economy in the world behind only the United States.

Amber Rudd, the United Kingdom’s Secretary of State for Energy and Climate Change, said: “The UK is not alone in its efforts to get the best deal possible in Paris, and this is a great opportunity for regional governments to show their commitment to tackling climate change. I whole-heartedly endorse this, and hope more subnational governments join those who have already signed up to tackle one of the biggest challenges of our time.”

The Under 2 MOU provides a template for nations to follow as work continues toward an international agreement to reduce greenhouse gas emissions ahead of this year’s United Nations Climate Change Conference in Paris. The agreement was first announced in May at a Sacramento event hosted by Governor Edmund G. Brown Jr.

“Our growing coalition is proof that California is in good company in combatting climate change and building our clean-energy economy,” said California Secretary for Environmental Protection Matthew Rodriquez. “A diverse group of cities, states and now nations from around the globe are ready to support ambitious commitments as we approach Paris this December.”

Under the agreement, subnational governments commit to either reduce greenhouse gas emissions 80 to 95 percent below 1990 levels by 2050 or achieve a per capita annual emission target of less than 2 metric tons by 2050. These targets allow each individual government to tailor emission reduction plans to fit regional needs.

National governments can endorse the MOU, and may indicate a range of support as endorsing partners. For instance, a nation can indicate its commitment to support subnational jurisdictions within its boundaries in their efforts to reach emissions targets, to encourage subnational governments to sign the MOU, or to limit national GHG emissions.

The Netherlands, host of today’s event, has a long history of collaboration with California on climate change and clean transportation. In 2013, they signed a Letter of Intent to cooperate on these issues. And in August, California and The Netherlands, alongside Quebec, also announced their intention to form the International Zero Emission Vehicle Alliance to accelerate global adoption of ZEVs.